1. Field of the Invention
This invention relates to devices for preventing the image from being shaken by unexpected vibrations and, more particularly, to optical systems of the zoom type which optically stabilize the image.
2. Description of the Related Art
If the photographer intends to take pictures while riding in a running car, flying aircraft, or other moving vehicle, he will suffer from vibrations propagating to the photographic system. Particularly when the exposure time is long, the taken picture has a largely shaken image.
In the past, image stabilization optical systems having the capability of preventing a shake of an image to be shot have been proposed in, for example, Japanese Laid-Open Patent Application No. Sho 50-80147, Japanese Patent Publication No. Sho 56-21133 and Japanese Laid-Open Patent Application No. Sho 61-223819.
In Japanese Laid-Open Patent Application No. Sho 50-80147, the zoom lens has two afocal variable magnification systems, wherein the image magnification is varied by using either of the two variable magnification systems in such a way as to have the relationship: M.sub.1 =1-(1/M.sub.2) where M.sub.1 is the angular magnification of the first variable magnification system and M.sub.2 is the angular magnification of the second variable magnification system, whereby the second variable magnification system is spatially fixed so as to compensate for a shake of the image. Thus, stabilization of the image is achieved.
In the Japanese Patent Publication No. Sho 56-21133, the vibratory state of the optical instrument is detected by a detecting means and the output signal from the detecting means is used to stabilize the image in such a way that part of the optical system, or an optical member, is moved in a direction to cancel the vibratory displacement of the image.
In the Japanese Laid-Open Patent Application No. Sho 61-223819, the photographic system is constructed with inclusion of a refraction type variable angle prism arranged at the frontmost position so that as the photographic system vibrates, the vertex angle of the refraction type variable angle prism is made to vary to deflect the image. Thus, good stability of the image is achieved.
In general, with respect to the mechanism which vibrates part of the photographic system, or a lens group, to compensate for the image shake from the intended line of sight to obtain a stationary picture, there is requirement for a photographic system of so simple a form that the relationship between the amount of compensation for the image shake and the amount of movement of the compensating lens is simplified, and the time it takes to compute the transformation is reduced to a minimum.
However, in the variable magnification optical system, the amount of image shake (image deflection) .DELTA.Y on the image plane relative to the angle of inclination .theta. of the variable magnification optical system becomes large in proportion to the magnification varying position, i.e., the focal length. Also, the ratio of the amount of image shake .DELTA.Y to the amount of decentering E of the compensating lens in the direction vertical to the optical axis, i.e., the decentering sensitivity S, will differ with different magnification varying positions.
Where the so-called zoom section having one of the lens groups arranged behind the first lens group changes its magnifying power during the variation of the image magnification and is used in part as a compensating lens group, minimization of the size of the whole lens system becomes easier. However, the required amount of decentering E of the compensating lens group relative to the amount of image shake .DELTA.Y varies to a large extent according to the function of the magnification varying position. For this reason, there is a problem that the structure of the image stabilization system becomes complicated.
As a related art of the invention, there is U.S. patent application Ser. No. 261,231 filed on Oct. 24, 1988.